Catalytic converters have been used to reduce emissions in exhaust gases of internal combustion engines for many years. For example, catalytic converters have been required for use in gas powered cars to remove hydrocarbons, nitrogen oxide, carbon monoxide, and other contaminants from exhaust gases. Catalytic converters have also been developed to provide auxiliary heat to the passenger compartments of hybrid cars. A typical catalytic converter includes a catalytic element, such as a catalytic core, contained in a housing. The catalytic element can be a monolithic catalyst with an open-pore structure having irregular and inter-connected flow paths for the exhaust gases, such as porous metal or ceramic materials, networks, or fiber structures. Other catalytic elements can have a honeycomb structure with regular flow channels through which the exhaust gases flow. The catalyst can be platinum, ruthenium, or another suitable catalyst that removes the undesirable elements from the exhaust gases. In general, the catalysts require a minimum temperature to react with the emissions, and higher reaction temperatures enhance the removal of emissions from the exhaust gases. Several conventional catalytic converters are relatively inefficient because the temperature at the center of the core is often much higher than at the periphery. As a result, the peripheral portions of the catalytic element typically have a lower reaction rate and lower efficiency that reduces the overall efficiency of the catalytic converter.
Although catalytic converters have been required in cars for many years, they have not been required in marine vessels with inboard or stern drive engines. However, in 2009, catalytic converters will also be required in new marine vessels with inboard or stern drive engines. This requirement is challenging because it has been difficult to maintain a sufficiently cooled exterior temperature for marine applications while also maintaining a sufficiently high temperature in the peripheral regions of the core to remove enough emissions to meet the standards of the Environmental Protection Agency (EPA). The core temperature of conventional catalytic converters is typically 1,000-1,400° F. In automobile applications the exterior surfaces of the catalytic converters are air cooled and have temperatures of about 600-1,000° F. Such high exterior temperatures significantly exceed the 200° F. exterior temperature limit set by the United States Coast Guard in its regulations for marine vessels. Catalytic converters for marine vessels are accordingly water cooled to reduce the exterior temperatures to within acceptable limits. Water cooling the exterior of the catalytic converters, however, further reduces the temperatures of the peripheral regions of the catalytic cores. Water cooled catalytic converters accordingly often have much lower efficiencies that result in higher hydrocarbon, nitrogen oxide, and carbon monoxide emissions.
One proposed solution for marine catalytic converters has a core contained in a housing, a solid insulating blanket of asbestos or other solid material around the core, and a water jacket around the insulating blanket. To offset the heat loss at the periphery of the core, marine catalytic converters may use more efficient and more expensive ruthenium catalytic elements. Although this solution is an improvement, it is still less efficient than catalytic converters for automobiles that use less expensive platinum catalytic cores. Moreover, although ruthenium or other core materials can be used to increase the efficiency, marine catalytic converters still may not meet the standards of the EPA.
Additionally, even though current catalytic converters reduce the emissions from cars and other sources, the sheer number of vehicles in operation have greatly contributed to the amount of hydrocarbons, nitrogen oxide, and carbon monoxide in the atmosphere. According to many studies and models, the rapidly increasing levels of hydrocarbons, nitrogen oxide, and carbon monoxide emissions are contributing to an unprecedented rate of global warming that will likely have many repercussions. The rapid increase in the average temperatures being reported have led many scientists to predict disastrous consequences unless emissions are reduced significantly. Therefore, providing a high-efficiency catalytic converter that removes more emissions from exhaust gases will protect the environment and mitigate the potential consequences of global warming.